One important property of a modern surfboard we often overlook is flex. This is now a hot topic in surfboard design. Surfers are starting to understand how surfboard flex affects our surfing and which design characteristics increase flex memory. Shapers everywhere are responding to this increased interest.
Flex allows your surfboard to build energy through turns when the surfboard’s materials change shape. Picture this sequence: You drop into a fast, steep bottom turn. As you do so your surfboard’s foam will bend into the turn. This results in more rocker and stored energy. As you come out of this turn and aim for the lip the foam snaps back to its original shape, releasing the stored energy and shooting the surfer out of the turn. A seasoned surfer will turn this burst of energy into acceleration, propelling himself into the next maneuver. While the flex characteristics can help your surfing, creating a surfboard design with flex in mind presents challenges. First, the surfboard must walk the line between flex and strength. Secondly, after repeated compression and expansion, a surfboard’s traditional wood stringer will weaken, giving it a “dead” feeling.
The recent emphasis on flex resulted in questions regarding stringer placement. A board with a center stringer will be stronger and less flexible along the center. However, its rails will flex and wobble which can cause the board to slow. This is called torsion flex. The closer the stringer is to the rail, the more strength or spring it will have along its perimeter which is where the board primarily makes contact with water in turns. It also supports the rail to maintain more of its original rocker shape while the flex comes from the center of the board.
The deck is the top of the surfboard. The surfboard rails often impact the deck design. The most common are domed, flat, and step decks. Each has its own benefits, performance characteristics, and feel. A number of companies now offer soft top surfboards. These lower the chance of injury and are incredibly durable without sacrificing too much performance. Some other deck options are Concave. Concave decks lower your center of gravity. Getting you closer to the surface of the wave. Other options are a S-deck, these decks are not flat from tail moving towards nose area. These decks have what appears to be a “Hump” in the center. Scooped out in nose area and pulled down tail.
The Surfboard Bottom Contour is easily one of the more complex and misunderstood concepts pertaining to surfboard design.
Basically the bottom contour purpose is to influence the way the water (wave) flows beneath it.
The contour will decide how fast or slow a surfboard goes and the ability to control and turn it.
This was used on the first surfboards. It literally means flat, no contour whatsoever.
Flat Bottoms are good for slow mushy waves and they respond well in these type of conditions, surf them in powerful or big waves and these will be difficult to control.
Like the fins, tail design is a highly argued yet innovation friendly aspect of a surfboard. To name all of the tail shapes that have passed before us since surfboard shaping went full throttle more than forty years ago would be exhausting. There are a few, however, that have come and stayed and will always remain. Squaretail, Swallowtail, Squashtail, Thumbtail, Rounded Pintail, Pintail, Battail, Diamond Tail, Double-wing swallow, Asymmetrical Tail and more i.e.
The 2+1 denotes a larger center fin (for reference, larger than a thruster center fin) with 2 small to medium-small fins at a position close to thruster rail fin positions. The “sidebites” contribute some lift, control, and stability to the board when it is “on rail,” arcing through turns. Typically, “sidebites” are removable, so the surfer can take them out for use in smaller waves, which gives less drag and freer turning. The 2+1 is a popular configuration for mid length to long boards.
Eps material has been around since the 50′s. Eps for surfboards came from large blocks of partially fused beads , primarily used for insulation and packaging. Hence the beer-cooler reference. The blocks of foam were something on the order of 3’by 4’ by 12’. Blanks were cut from the big blocks with a hot wire. EPS must be glassed with epoxy. Early epoxies got a bad rap for being highly toxic if not handled right. They were also not very clear and tended to be more on the yellow or light brown side of things.
In the early 80′s a handful of board builders revisited eps. The foam hadn’t really changed much. There was a lot of interest in EPS/Epoxy construction for sailboards. The strength to weight advantages were obvious in these larger watercraft. It became the go to construction for most of the custom sailboard builders. This know-how trickled into the surfboard world. The ASP tour actually had an event in 1985 that was held in a wave pool in Allentown, Pa. Tom Carroll won the event. Quite a few pros ordered up lightweight epoxy boards for this fresh water event. Now we are using surfboard specific eps foam. It is highly fused and has a much smaller bead size than the foams that were experimented with by earlier generations of board builders.
Is Eps more buoyant?
2 boards of equal volume and area, if one is lighter, that is basically your gain.
With EPS cores it usually works out to a 10 to 15% difference. and feels much livelier when surfed.
Eps foam requires glassing with epoxy resin. Epoxies are much more durable than polyester resin. They also come in a variety of flex matrices and the combination creates a very durable, light weight surfboard.
What are the differences between the two?
PU is considered an open cell foam (counterintuitive) and is basically a plastic foam filled with irregular gas bubbles. When a PU core is expose to water, it takes a while to migrate and over time the foam will also deteriorate.
EPS is considered an open cell foam…think many tiny ping-pong balls stuck together. The trick is to compress and fuse the little beads together so water doesn’t have the ability to migrate freely.
PU can be glassed with either polyester resin or epoxy. In fact, PU with an epoxy glass job is a much more durable alternative to the poly.
EPS must be glassed with epoxy.
What about dings?
With EPS/epoxy boards, small dings where there isn’t too much of the core material exposed, it is ok to use a quick acting UV cure poly. Solarez does make a UV “Epoxy”. For larger wounds, you need to use epoxy. Polyester resin will melt the EPS foam.
Yes if left unrepaired, it will take in LOTS of water. The ding repair guys love this. They often drain water for days.
What about flex?
EPS foam glassed with epoxy resin is not stiff. If anything, all else being equal, it will be more sensitive and have quicker springback than a PU/PE board. In fact, because of the lightness/buoyancy you can go thinner if you choose, which will make the board feel more alive. Epoxies also come in a variety of flex matrices and the potential to tailor flex to personal taste is wide open.
Certain types of molded EPS/epoxy boards have a layer of high density sheet foam sandwiched between the core, cloth, and resin. This is what causes those types of molded board to be “stiff” feeling.When deciding on which core material to use, consider your local conditions. In everyday surf, smaller weaker waves, light wind, the lightness and liveliness of EPS/Epoxy should be a no-brainer.
Why don’t you see more EPS in the stores?
Cost: Part of it is price point. The cores don’t differ much in price. It’s the epoxy resin that is more expensive and through-put time also affects cost…it’s a little harder to work with and takes longer to go through the factory than PU/Poly.